A conventional bow exercise device is disclosed in FIGS. 7 and 8, and generally includes a plurality of flexible sticks 40 as shown. The stick 40 includes a cylindrical body 41 and a base 43 is connected to a lower end of the body 41 so as to be fixed to a frame which is not shown, and a top cap 42 is connected to a top of the body 42. The top cap 42 has a lug 421 with a hole 422 defined through. A rope (not shown) is tied to the lug 421 at the hole 422 and pulled by the users. The users have pull the rope to bow the body 41 so as to exercise the muscles. Nevertheless, the body 41 has a fixed flexibility so that the resistance force of the body 41 cannot be adjusted. In other words, the exercise device has to equip a plurality of sticks 40 of different diameters and flexibility. Besides, due to the integral structure of the stick 40, the diameter of the stick 40 has to be increased if a larger resistance is required, and this involves a high cost.
The present invention intends to provide a stick that includes at least one flexible plate which has one end movably inserted in the top cap such that the stick has better flexibility.